HbA1c Testing Does Not Require Fasting
HbA1c samples can be collected at any time of day without fasting, making it highly convenient for both patients and clinical practice. 1, 2
Why Fasting Is Not Required
- HbA1c reflects average glycemia over approximately 2-3 months, representing long-term glucose exposure rather than a single point-in-time measurement 1, 3
- The test result is not affected by short-term factors including recent food intake, exercise, stress, or acute illness 1, 2, 3
- This is a major advantage over fasting plasma glucose or oral glucose tolerance tests, which require specific patient preparation and timing 1
Clinical Advantages of Non-Fasting Collection
- Greater convenience compared to fasting plasma glucose measurements, as HbA1c does not require patients to fast 1
- Can be drawn during any clinical encounter, including acute care settings, without concern for the patient's recent meal status 2
- Greater preanalytical stability and fewer day-to-day perturbations during stress, changes in nutrition, or illness compared to glucose measurements 1
- Lower within-person variability than glucose-based tests 1, 3
Important Caveats
While fasting is not required, certain conditions can affect HbA1c accuracy:
- Conditions that falsely elevate HbA1c include iron deficiency, vitamin B12 deficiency, and splenectomy, which prolong red blood cell lifespan 2
- Conditions that falsely lower HbA1c include erythropoietin therapy, iron/B12 supplementation, chronic liver disease, splenomegaly, and pregnancy, which increase red blood cell turnover 2
- Do not use HbA1c in patients with sickle cell disease (HbSS), other homozygous hemoglobin variants, recent blood transfusion, hemolytic anemia, or conditions affecting red blood cell turnover 1
- In these situations, use plasma glucose criteria or alternative tests like fructosamine instead 1